1. Field of the Invention
The present invention relates to a method for forming a thin film and systems for the same, and more particularly a method for forming a thin film for a barrier metal and systems for the same.
2. Description of the Relevant Art
A contact region in LSI has a diffusion layer on the surface of a substrate as a base, connected with an interconnection such as Al through a contact hole.
However, as shrinkage and high integration of LSI are proceeding, the diffusion layer is becoming shallower, which causes such problems as in said shallow diffusion layer, Al spike occurs and breaks junction, or Si precipitates on the bottom of a contact hole, leading to an increase in contact resistance.
In order to solve these problems, Al alloys (e.g. Al-1% Si)previously contaminated with about 0.5-2% of Si are used as electrode connection material. Recently, however, even these Al alloys are becoming insufficient to prevent precipitation of Si, as the diameter of a contact hole is getting smaller than before.
Accordingly, forming a thin film called a barrier metal between Al alloy and a Si substrate for preventing diffusion has been considered. A TiN film is noticed as a barrier metal on account of its low electrical resistance material and chemical stability (Yamanishi, Yoshihara, Kitahara and Hosokawa; "Vacuum", Japan, vol.30, No.5, p347, 1987).
It is desirable that material for a barrier metal should have small barrier height to both p .sup.+ Si and n .sup.+ Si fundamentally. As shown in Table 1 below, however, a TiN film has high contact resistance to a Si diffusion layer (especially high to p .sup.+ Si), so that forming a base film of such as Ti is required.
TABLE 1 ______________________________________ Contact Resistance of Barrier Metal And Silcide barrier n.sup.+ Si p.sup.+ Si metal and (.times. 10.sup.-7 N.sub.D (.times. 10.sup.-7 N.sub.D silicide .OMEGA. cm.sup.2) (cm.sup.3) .OMEGA. cm.sup.2) (cm.sup.-3) Ref. ______________________________________ W(CVD) 2.2 1E20 7E19 TiW 2.0 1E20 4.5 7E19 TiW/PtSi 1.2 1E20 3.6 7E19 TiN 1.8-2.7 44-8.9 21 TiN/Ti 0.4-0.5 7.0-8.9 21 TiSi.sub.2 0.8 2.3E20 700 1E19 22 NiSi 0.5 2.3E20 200 1E19 22 Pd.sub.2 Si 0.7 2.3E20 30 1E19 22 ______________________________________ (Saito; "Semicon Seminar", Japan, June, 1987, p181)
A Ti film is usually formed by sputter method with a Ti target. Few examples of forming a Ti film by CVD methods (thermal CVD method, plasma CVD method) have been reported.
Besides, the formation of Ti by using plasma has been reported (Narutomi; "Titanium Zirconium", vol.24, No.3, July, 1976, pp.130-144). This comprises reducing a halogenide product of Ti (TiCl.sub.4) to titanium with a reductant such as hydrogen by using an arc plasma jet, wherein supply of material into a plasma jet torch of 2000.degree. C. is required. In addition, it says that in the case of using argon hydrogen plasma for reduction of TiC.sub.4 (Krapukhin & Korolev, 1968), fine powder of titanium may be obtained, which no one has even tried.
As described above, a TiN film is an effective material for a barrier metal of LSI. However, a TiN film has high contact resistance to a Si diffusion layer, so that forming a base film of such as Ti is required.
Although a Ti film is usually formed by sputter method as mentioned above, forming a Ti film by sputter method has poor step coverage. Therefore, as shrinkage of a contact hole proceeds, leading to higher aspect ratio, little Ti deposits on the bottom of the contact hole, as a result, this method cannot be applied to LSI which is getting finer.
Since deposition by LPCVD (low pressure chemical vapor deposition) method generally has good step coverage, the deposition of a TiN film by LPCVD method has been studied. On the contrary, since deposition of a Ti film needs high energy for reduction of TiC.sub.4, it is impossible to form a Ti film by LPCVD method in which reaction is caused by only thermal energy.
And since forming Ti by an arc plasma jet is high temperature treatment over 2000.degree. C., it is impossible to include such high temperature treatment in the process of producing LSI, by which only powder of Ti has been ever obtained.